Wolf is a believer in the top-down approach. In other words, we start
by building small things, then we build very small things, and we keep
on working downward in size, until we eventually end up at the atomic
level. The NNF is currently exploring projects ranging from ultra-fast
gallium- arsenide logic gates to chips that incorporate miniaturized
sensors carved out of silicon. There are immediate applications for
this kind of device. The mechanism for locking seat belts in a car,
for instance, will soon be based around a chip that contains its own
ultra-tiny motion sensor, like a miniaturized pea rattling in a pod.

This is real, and it's practical, but it doesn't have the power and
promise of nanotechnology, a word that now has at least two different
meanings. To clarify matters, Drexler now talks about "molecular
nanotechnology" to describe the process of moving molecules
individually to create more complex structures (the bottom
up-approach).

>From listening to Wolf, it quickly becomes clear that top-down
advocates such as he have formed a faction that's violently opposed to
the bottom-up approach. Wolf tries to be nice about it, but his
impatience is evident. "The fact is," he says, "we have no idea how to
do 3-D assembly. I don't want to demean anybody, but nanotechnology
has been oversold, in the sense that it's been popularized."

What's so bad about popularization?

"Let me put it this way. As scientists, we all have great
imaginations. But most of us are a little more cautious about speaking
out."

Meanwhile, on the other side are scientists like David Blair, a
biologist at the University of Utah. "I have a lot of respect for Eric
Drexler," he says. "He's a visionary."

Blair is studying one of the smallest, most complicated, most
fascinating objects in the natural world. It's an incredibly tiny
motor, one-fourth the size of the robot arm that Merkle and Drexler
would like to build. It also happens to be up and running. It's made
of protein, and the amazing thing is, it grows naturally as a
component of common, ordinary bacteria.

Like any cells, bacteria must eat to survive. Somehow (no one knows
how) they detect nearby nutrients and swim toward them. Their means of
propulsion is the flagellum, which consists of a corkscrew-shaped
filament attached to the nanomotor. It spins the filament at about
15,000 rpm, propelling bacteria in the same way that outboard motors
propel boats. Make no mistake, this genuinely is a motor. There's a
stator and a rotor, just as in a motor that turns an electric fan.

Using desktop simulation, Drexler and Merkle are building a tiny
robotic arm one atom at a time,...

...but nature has already accomplished a remarkable feat of
nanotech: the common bacteria's flagellum.

Blair would like to take the motor to pieces, but he has no tools tiny
enough for the job. So, he uses an indirect method, selectively
damaging the proteins that the motor grows from and watching how it
malfunctions. "We're like auto mechanics who only have hammers to do
our work," he says. "But I think we may learn interesting lessons for
the design of man-made motors some time in the future."

A more precise tool for investigating the nanorealm is the scanning-
tunneling electron microscope (STM), which uses a super-sharp, servo-
controlled tungsten tip to measure the size of individual atoms on a
hard, flat surface. The STM is unsuitable for tracing the contours of
soft bioforms, but its powers have been amply demonstrated in other
areas. In 1990, Don Eigler attracted global publicity when he used his
STM to push individual xenon atoms around so that they spelled out the
initials of his employer, IBM. Eigler is now reportedly pushing carbon
and oxygenatoms together to create carbon monoxide, but to advocates
like Ralph Merkle, this kind of work is just the first step down a
long road. Using today's STMs to manipulate molecules, says Merkle,
"is like trying to build a wristwatch with a sharpened stick."

However, an exciting new development in the STM world has come from an
unlikely source. A graduate student named Mark Voelker, at the Optical
Sciences Center of the University of Arizona at Tucson, has built the
nation's first dual-tip scanning-tunneling electron microscope.

Voelker is shy and soft-spoken, and he describes himself as "just
another science nerd." But he seems to have a practical,
do-it-yourself side to his personality. He enjoys hanging out in pool
rooms, and he drives a rebuilt 1970 Corvette. "I blueprinted the car,"
he says, in his placid, low-key style. "That means I completely
disassembled the engine, measured every part, and machined them to
adjust the tolerances. Then I put everything back together
again."